In the field of ultrasound transducers the use of piezoelectric transducers such as lead zirconate titanate (PZT) transducers and, nowadays, MEMS transducers such as capacitive micro-machined ultrasound transducer (cMUT) devices is common practice for providing two or three dimensional ultrasound waves. The micro-machined technology in this field allows small feature sizes and the realization of high-frequency beam-forming arrays, which can be formed monolithically on the same wafer.
The existing ultrasound transducers have a limited power factor and a limited efficiency due to a limited coupling factor. The coupling factor of ultrasound transducers represents a ratio of the stored and delivered mechanical energy to the total electrical energy in a lossless vibration cycle. Common coupling factors of cMUTs are in the range of 50%, while the effective coupling sector could be even lower. Practically, the transducer driver circuit has to provide more electrical energy to the transducer than the amount of acoustic energy which is delivered by the transducer. The remaining energy is conserved in the reactive parts of the transducer or is dissipated in the resistive parts and converted into lost heat. The conserved energy, which is mainly capacitive electrical energy, may be delivered back to the driver circuit and depending on the driver type, the energy can be reduced during a following vibration cycle or is dissipated in the driver circuit.
A common method to conserve energy at the driver device is to use an additional reactive device, i.e. an inductor, which operates in terms of energy storage in anti-phase with the transducer. In the case of two dimensional transducer arrays having discrete driver electronics, the discrete inductors are used in series with the driver. For three dimensional ultrasound arrays including thousands of transducers and in the case of integrated electronics, the respective inductors would strongly increase the overall size of the driver device.